Mare Winningham to Guest-Star on CBS' Under the Dome

Winningham will play Agatha, a seemingly warm woman acting as a caretaker for a house. She'll even welcome Big Jim (Dean Norris) into the home, but we'll learn that her intentions are anything but sincere as we discover her ties to the town.

"I'm thrilled to be working with Mare Winningham on Under the Dome," said executive producer Neal Baer. "She's my good-luck charm: I worked with her on ER, as well as on Law & Order: SVU (for which she was Emmy-nominated as Best Guest Actress). She brings truth and believability to every role and she will definitely leave viewers talking."